Thermal head

ABSTRACT

The present invention has an electrode for energization use of a thermal head having an unprecedentedly new electrode construction of a full peripherally surrounding type, so that one heating portion corresponds to one individual electrode without separation or independence of a heating resistor. Thus, the heating efficiency in the printing operation is improved to increase the thermal response property, thus making it possible to save the power. Furthermore, the full periphery surrounding electrode portion is adapted to be completely covered by the heating resistor to remove the dispersion of the resistance values of each dot responsible for the dispersion of the printing width of the heating resistor, and to completely provide uniformity by an energization overload trimming system. The heating efficiency and the thermal response property are improved, and the uneven printing concentration of each dot is removed to make the gradation recording property better, thus making it possible to have an embodiment of a thermal head capable of high-quality printing and having high reliability.

BACKGROUND OF THE INVENTION:

The present invention generally relates to a thermal head which is usedin a thermal transfer recording apparatus, a heat sensitive recordingapparatus, etc. for printers, facsimiles, etc.

Conventionally, the thermal transfer recording apparatus and the heatingsensitive recording apparatus for printers, facsimiles, etc. effect theheat sensitive recording with respect to a heat sensitive paper or anordinary paper with an ink sheet superposed thereon by the use of athermal head. The thermal head to be used in printing apparatuses suchas a thermal transfer apparatus, thermally sensitive printing types ofprinters, etc. is two in types as follows. A first one is a so-calledthin membrane type, wherein heating resistors, electrodes forenergization use and abrasion-proof layers are formed by a vacuum thinmembrane forming process such as evaporation, sputtering on aglaze-alumina base plate so as to form patterns by the use of aphotolitho etching method. A second one is named so-called thickmembrane type, wherein electrodes for energization use, heatingresistors, and abrasion-proof layers are respectively formed on aglaze-insulation base plate by the printing burning of the paste.

The above-described two types of thermal heads have advantages anddisadvantages respectively. Namely, as the thin membrane type of thermalhead is uniform in its resistor shape (area, thickness, etc.) among therespective dots, with its thermal capacity being uniform, the heattransfer into the paper is uniformly effected during the printingoperation. Also, as the resistance values of the respective resistorsare obtained uniformly up to some extent, and the thermal head iscollectively superior in the print quality. As the thickness of theresistor is as thin as 1000 to 5000 Å, the thermal capacity is smaller,with the constant becoming superior, the print heating efficiencybecoming higher during the rising and falling operations of the resistortemperature during the on and off pulse application. However, in theconventional thin membrane type, it is difficult to have the dispersionof the resistance value at ±5% or lower, so that a more superior printquality is hard to obtain. Also, there are many problems to be solved interms of productivity, lower cost such as facility cost, batchproduction, etc. for the thin membrane process.

On the other hand, it is noteworthy that the thick membrane type ofthermal head has many advantages such as lower facility cost and easiercontinuous production, because it uses a print burning method.

FIG. 5 is a construction view of the conventional thick membrane type ofthermal head. A glaze layer 2 is formed on the top face of an aluminabase plate 1. A common electrode 3, an individual electrode 4 and aheating resistor 5 are formed on it, with an abrasion layer 6 beingprovided to cover the respective one portion of the heating resistor 5,the electrodes 3, 4.

FIG. 6 is a plan view showing the electrode shape of the conventionalthick membrane type of thermal head. As it is difficult to independentlyconstitute the heating resistor in the thick membrane type of thermalhead, a line-shaped common heating resistor 5 is provided, with theconductive electrodes for energization use 3 and 4 having the commonelectrode 3 and the individual electrode 4 introduced and exposed in azigzag shape, alternately from both the sides of the heating resistor 5.Also, one dot is constructed in one individual electrode 4, with twoheating portions 7a and 7b being provided correspondingly. Namely, uponthe application of voltage in pulse upon between one individualelectrode 4 and a common electrode 3,, a current flows at the same timeto the heating portions 7a and 7b to form two color forming points.

Conventionally the resistor values of the heating member of the thickmembrane type thermal head having the electrode shape of the zigzag typehave the dispersion of ten-odd percent in a plurality of dots within thesam head. The major causes for the resistance value dispersion lay innonuniformity in the dispersion condition, etc. of the heating resistormaterial, and printing accuracy in uniformity, etc. of the line width,thickness of the line-shaped common heating resistor 5. Namely, in thethick membrane type of thermal head, it is difficult to uniformly printthe line width of the line-shaped common heating resistor 5 enough tohave several percent of dispersion, so that the contact area between theelectrodes 3 and 4 for energization use introduced, disposed from boththe sides of the heating resistor 5 and the heating resistor 5 isdifferent, thus resulting in fundamentally increasing the dispersion ofthe respective dot resistance values.

Therefore, the resistance value of the dot may be uniformly adjustedinto approximately ±1% through a trimming operation by the use of anenergization overload trimming system (a method of using the resistancevalue variation through self-generating Joule heat to be caused when thepower is fed into the heating resistor), but the calorific value perunit value of the heating resistor can not be made uniform.

SUMMARY OF THE INVENTION

Accordingly, an essential object of the present invention is to providea thermal head, the invention relating to an energization electrodeshape of the thermal head, characterized in that the electrode shape hasa construction of an approximately full periphery surrounding type ofelectrode unprecedentedly new, with the object of improving the heatingefficiency in the printing to improve the thermal response propertiesand to save the power. Namely, it is possible to correspond one heatingportion with respect to on individual electrode without the separationand independence of the heating resistor.

Another important object of the present invention is to provide athermal head of the above-described type, which is characterized in thatthe approximately full periphery surrounding type of electrode portionis adapted to be completely covered by the heating resistor to removethe dispersion of the respective dot resistance value responsible forthe dispersion of the printing width of the heating resistor, and toarrange it completely uniform by the energization overload trimmingsystem.

The above-described effects may provide a thermal head which is betterin heating efficiency, thermal response property, is capable ofhigh-quality printing by the improvements in toner recording propertythrough the removal of uneven printing concentration of the respectivedots, and is extremely reliable.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present invention willbecome apparent from the following description taken in conjunction withthe preferred embodiment thereof with reference to the accompanyingdrawings, in which:

FIG. 1 is a sectional schematic view of a thermal head in one embodimentof the present invention;

FIG. 2 through FIG. 4 show a plan view showing an electrode constructionthermal head;

FIG. 5 is a sectional construction view of a conventional thermal head;and

FIG. 6 is a plan view showing the electrode construction of the thermalhead of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Before the description of the present invention proceeds, it is to benoted that like parts are designated by like reference numeralsthroughout the accompanying drawings.

Embodiment 1

As shown in the sectional construction view of FIG. 1, and in the planview of FIG. 2, a common electrode 10 and an individual electrode 11made of a gold conductor (0.5 through 1.0 μm in thickness) are providedat an interval of dot pitch (16.7 μm) on an alumina base plate 8 with aglaze layer 9 provided thereon. The electrode construction at this timeis one wherein the power introduction portion of the common electrode 10is disposed on approximately the full periphery of the powerintroduction portion of the individual electrode 11 as shown in FIG. 2,namely is an electrode construction of an approximately full peripherysurrounding type. The heating resistor 13 (4 through 8 μm in thickness),mainly made of Ru02, is print-burned in line shape (350 μmin width),with the heating resistor 13 being formed on the opposite portion of theelectrode group. A glass layer is burned so as to cover one portion ofthe resistor and the electrode group, so that an abrasion-proof layer 12(4 through 8 μm) in thickness is formed.

The resistor values of respective heating portions to be formed betweenthe opposite common electrode 10 and the individual electrode 11 afterthe head formation are 1500Ω±7%, although they are different in theelectrode width of the opposite portion. It is to be noted that the endportion of the common electrode 10 is swollen into a common electrodeswollen portion 14, with one portion of the individual electrode 11having a narrow portion 15. The reference numeral 16 is a hollow portiondisposed in one portion of the common electrode.

By the use of the energization overload trimming method for adjustingthe resistor value through the self-generating Joule heat of the heatingresistor, the pulse voltage (5 through 150 V, several μs) is energizedfor an optional time period onto the respective heating portion to beformed between the electrodes of a pair of opposite common electrode 10and the individual electrode 11 so as to separately adjust the resistorvalues of the respective heating portions for the arrangement of theresistor values of all the heating portions within ±1%.

The conventional head with only the electrode pattern being supposed tobe the conventional zigzag type of electrode pattern for comparison ofthe head is driven on the conditions of 0.4 W/Dot, 1/4 duty, 16 ms/cycleto print on heat sensitive paper. According to the results of theconcentration of the color forming point of the respective dot measuredby a micro densitometer, the conventional head has a dispersion of ±5%or more in the concentration of the color forming point, while the headof the present invention has the dispersion within ±2%, thus allowingthe extremely high quality of printing operation.

It has been found that the head with the construction of the end portionof the electrode of the electrode group for introducing the heatingpower into the heating member having the construction of the electrodeof an approximately full periphery surrounding type is 1.2 times as highin the printing concentration as compared with the head of conventionalsimple zigzag type of electrode pattern, and is superior in the thermalresponse properties. Also, the printing condition in the actual printingallows the extremely high quality of printing to be effected as comparedwith the conventional simple zigzag type of head, because the colorformation of the first line is clear.

It is confirmed that the heads of the full periphery surrounding typeelectrode constructions in FIG. 3 A, B, and C as the electrode shapealso have a similar effect. Also, the cross talk between the adjacentdots may be almost neglected. It is to be noted that in FIG. 3, the samereference characters are given to the element of the same names.

Embodiment 2

A heating resistor (0.5 through 8 μm in thickness) including Ru02 on analumina base plate with the glaze layer provided thereon is printed,burned in a line shape (400 μm in width) to form the heating resistor,and then a common electrode and an individual electrode each beingcomposed of a gold electrode (0.5 through 1.0 μm) are provided at aninterval of the dot pitch (16.7 μm). The electrode construction at thistime is one wherein the end portion of the common electrode was disposedon approximately full periphery of the end portion of the individualelectrode as shown in FIG. 2, namely, the electrode construction of anapproximately full periphery surrounding type.

Then the glass layer is printed and burned so as to cover the oneportion of the resistor and the electrode group to form theabrasion-proof layer (4 through 8 μm in thickness).

According to the results given about the head as in the embodiment 1,the extremely high quality of printing is effected, with the dispersionwithin ±2% in the printing concentration. Furthermore, it has been foundthat the printing concentration is 1.2 times high as compared with thehead of the conventional simple zigzag type of electrode pattern, withthe head being superior in thermal response property. Also, from theprinting condition in the actual printing operation, it is found outthat the extremely high quality printing may be effected as comparedwith the conventional simple zigzag type of head, with the first line ofcolor formation being clear.

Embodiment 3

FIG. 4 is a plan view for illustrating a thermal head in a differentembodiment of the present invention. As shown, the electrodes 19 and 20for energization use of the first group and the second group arecomposed of gold (0.5 through 1.0 μm) and are alternately introduced anddisposed onto the alumina base plate 18 provided on the glaze layer, aredisposed at an interval of dot pitch (167 μm). It is noted that theelectrodes 20 are connected with an individual electrodes or electrodeend portion, and the conductor electrode 19 are is connected with acommon electrode 21. The electrode construction at this time is onewherein the end portion of the first group of individual electrodes 20is disposed on the full periphery of the end portion of the electrode19. The end portion for the common electrode use of the second group isdisposed, namely, so as to provide the electrode construction of a fullperiphery surrounding type. Note the perpendicular portions extendingsubstantially perpendicularly from the electrodes 19 between the pointwhere the electrodes 19 are connected to common electrode 21 and theends thereof. Then, the resistance material for heating use, mainlycomposed of Ru02, is printed and burned in a line shape (350 μm inwidth) on the opposite portion of the electrode group so as to form aheating resistor 22 (4 through 8 μm in thickness). Then a glass layer isprinted and burned so as to cover one portion of the resistor 22 and theelectrode group to form an abrasion proof layer 23 (4 through 8 μm inthickness).

Then, by an energization overload trimming method for adjusting theresistance value by the self-generating Joule heat of the heatingresistor, the pulse voltages (5 through 200 V, several μs) are energizedfor an optional time, separately into the respective heating portions,for example, 24a and 14b to be formed between the conductor 12a of theindividual electrode and a pair of adjacent conductor electrodes 13a forcommon electrode use so as to separately adjust the resistance value ofthe heating portion for arrangement of the resistance values of all theheating portions within ±1%.

After the adjustment of the resistance values the one portion of theelectrodes of the second group is connected with the electrode group ofthe second group through printing and burning of the conductive materialof a Cu - resin series as shown in a plan view showing the electrodeshape of the thermal head in the drawing so as to form the commonelectrode 21.

It is to be noted that the resistance value of one dot is a composedvalue between the heating portions 24a and 24b to be formed between theend portions of a pair of electrodes 19 adjacent to the end portion ofthe individual electrode 20 as the second group of electrode groups isturned into the short condition by the common electrode 21. In this caseof the present embodiment, the composed resistance value of the heatingportion is 1500±1%.

The conventional head with only the electrode pattern being theconventional zigzag type of electrode pattern for the comparison of thehead is driven under the conditions of 0.4 W/dot, 1/4 duty, 16 ms/cycleto print on the heat sensitive paper, according to the results givenabout the concentration of the color forming point of the respectivedot. The conventional head has a dispersion of ±10% or more in theconcentration of the color forming point, with the head of the presentinvention having the dispersion within ±1.5%, with the printing beingextremely high in quality.

Furthermore, the head with the construction of the end portion of theelectrodes of the electrode group to be introduced into the heatingmember being a full periphery surrounding electrode construction is 1.2times as high in the printing concentration as compared with the head ofthe conventional simple zigzag type of electrode pattern, thus beingsuperior in thermal response property. Also, from the printing conditionin the actual printing operation, the first line color formation isclear and the extremely higher quality of printing may be effected ascompared with the conventional simple zigzag head.

If the electrode shape is in the construction of the peripherysurrounding type electrode with the common electrode end portion beingprovided on the periphery of the individual electrode end portion, asimilar effect is obtained, and there is not, needless to say, anyrestriction to the embodiment.

Furthermore, as short materials for common electrode use, there may beused a resin series and a glass flit series containing metals of Cu, Ag,Ag - Pt, Ag - Pd, Ag - Pd - Pt, Au, etc.. Also, the formation may beeffected with the non-electrolytic metal plating of Cu, Ni, Au, Cr, etc.without any restriction to the above-described embodiment. Furthermore,the base plate of the thermal head may be an enamel one, and there isnot, needless to say, any restriction even to the respectiveconstruction materials of the head.

Embodiment 4

After the formation of an electrode layer (2000 through 7000 Å) Ni - Crby a vacuum thin membrane forming process like evaporation andsputtering on the glazed alumina base plate, the pattern formation ofthe full periphery surrounding type electrode construction like that ofFIG. 2 is formed by a photolitho etching method. Then a resistor layer(1000 through 5000 Å)of Ta - Si is formed in a line shape (350 μm inwidth) on an electrode construction portion of the full peripherysurrounding electrode by a vacuum thin membrane forming process.Furthermore, an abrasion-proof layer (3 through 7 μm) of SiC is formedto cover the resistor layer and the full periphery surrounding typeelectrode construction portion so as to manufacture the thin membranetype thermal head.

The head of the present embodiment is found to be 1.1 times as high inthe printing concentration as compared with the conventional thermalmembrane type of thermal head and to be superior in thermal responseproperty. Also, a similar effect is confirmed even in a case where theheating resistor and the electrode are formed upside down.

Furthermore, the present invention is not restricted to theabove-described embodiment. The base plate of the thermal head may be anenamel base plate, and furthermore the particular limit is not given,needless to say, with respect to the respective construction materialsof the head and the dot resistance value.

As described hereinabove, the present invention relates to the electrodeshape for energization use of the thermal head, and provides a thermalhead, which is improved in the heating efficiency in the printingoperation to increase the thermal response property and to save thepower, and is improved in uneven printing concentration of therespective dots for a better gradation recording property, is capable ofhigh quality printing operation, is and higher in reliability. Also,according to the present invention, the photolitho etching step of theresistor layer may be omitted even in the thin membrane type of thermalhead, thus making it possible to have the lower cost.

Although the present invention has been fully described by way ofexample with reference to the accompanying drawings, it is to be notedhere that various changes and modifications will be apparent to thoseskilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention, they wouldbe construed as included.

What is claimed is:
 1. A thermal head comprising:a base plate; a commonelectrode on said base plate, said common electrode having a pluralityof electrode end portions extending therefrom; a group of individualelectrodes on said base plate, said individual electrodes extendingbetween respective said electrode end portions of said common electrode;a heating resistor for energization by energization of said individualelectrodes together with respective said electrode end portions; andmeans for substantially surrounding the entire periphery of a said endportion of said common electrode or the entire periphery of a saidindividual electrode; wherein said means for substantially surroundingcomprises swollen portions on two said end portions of said commonelectrode adjacent a said individual electrode.
 2. The thermal head asset forth in claim 1, wherein:each of said individual electrodes has anarrowed portion; and said swollen portions on said end portions of saidcommon electrode extend from the ends of said end portions toward saidnarrowed portion of a said individual electrode.
 3. The thermal head asset forth in claim 2, wherein:said means for substantially surroundingfurther comprises perpendicular portions extending substantiallyperpendicularly from said electrode end portions from either sidethereof at a position between said ends of said electrode end portionsand said common electrode.
 4. The thermal head as set forth in claim 1wherein:said common electrode and said individual electrodes aredisposed on said base plate with said base plate on one side thereof andsaid resistor on the opposite side thereof; and an abrasion-proof layeris disposed covering said resistor and a portion of said group ofindividual electrodes.
 5. The thermal head as set forth in claim 1wherein:said resistor is disposed on said base plate; and anabrasion-proof layer is disposed covering said resistor and a portion ofsaid common electrode.
 6. The thermal head as set forth in claim 1,wherein:said common electrode on said base plate further comprises atleast one hollow portion.
 7. The thermal head as set forth in any one ofclaims 1, 9, 11 or 12, wherein:an abrasion proof layer is disposed onsaid heating resistor and said electrode end portions of said commonelectrode and said individual electrodes.
 8. The thermal head as setforth in any one of claims 1, 9, 11 or 12, wherein:an abrasion prooflayer is disposed on said heating resistor and said electrode endportions of said common electrode and said individual electrodes; andsaid heating resistor comprises a plurality of heating resistor portionscorresponding to respective electrodes of said first group of electrodeson said base plate, said heating resistor portions having resistorvalues determined by an energization overload trimming system.
 9. Athermal head comprises:a base plate; a common electrode on said baseplate, said common electrode having a plurality of electrode endportions extending therefrom; a group of individual electrodes on saidbase plate, said individual electrodes extending between respective saidelectrode end portions of said common electrode; a heating resistor forenergization by energization of said individual electrodes together withrespective said electrode end portions; and means for substantiallysurrounding the entire periphery of a said end portion of said commonelectrode or the entire periphery of a said individual electrode;wherein said means for substantially surrounding surrounds substantiallythe entire periphery of a said individual electrode and comprises twoend members extending from each said electrode end portion on eitherside of a respective said individual electrode.
 10. The thermal head asset forth in claim 9, wherein:said means for substantially surroundingfurther comprises perpendicular portions extending substantiallyperpendicularly from said individual electrode at a position spaced fromthe end of said individual electrode.
 11. A thermal head comprising:abase plate; a common electrode on said base plate, said common electrodehaving a plurality of electrode end portions extending therefrom; agroup of individual electrodes on said base plate, said individualelectrodes extending between respective said electrode end portions ofsaid common electrode; a heating resistor for energization byenergization of said individual electrodes together with respective saidelectrode end portions; and means for substantially surrounding theentire periphery of a said end portion of said common electrode or theentire periphery of a said individual electrode; wherein said means forsubstantially surrounding surrounds substantially the entire peripheryof a said individual electrode and comprises perpendicular portionsextending substantially perpendicularly from a said individual electrodeat a position spaced from the end of a said individual electrode.
 12. Athermal head comprising:a base plate; a common electrode on said baseplate, said common electrode having a plurality of electrode endportions extending therefrom; a group of individual electrodes on saidbase plate, said individual electrodes extending between respective saidelectrode end portions of said common electrode; a heating resistor forenergization by energization of said individual electrodes together withrespective said electrode end portions; and means for substantiallysurrounding the entire periphery of a said end portion of said commonelectrode at the entire periphery of a said individual electrode;wherein said means for substantially surrounding forms a part of a saidindividual electrode and surrounds substantially the entire periphery ofa said electrode end portion.
 13. The thermal head as set forth in claim12, wherein:said means for substantially surrounding comprises two endmembers extending from each said individual electrode on either side ofa respective said electrode end portion.
 14. The thermal head as setforth in claim 13, wherein:said electrode end portion has a narrowedportion thereon; and said means for substantially surrounding furthercomprises a swollen portion on the ends of said end members of saidindividual electrode, said swollen portions extending from said endmembers toward said narrowed portion of said electrode end portion.